It is generally known that from the electrical signal of the heart, the so-called EKG signal, individual heartbeats may be recognized and that various quantities describing the function of the heart may be measured from those. Usually, the EKG signal is measured by means of electrodes placed in various parts of the body on the skin surface. Quantities describing heart functions are, among others:
the number of heartbeats/minute that is the pulse
the difference in time between two heartbeats and its variations, that is the pulse interval
the total number of heartbeats during a certain performance/time period that is the number of pulses
In addition, quantities that may be monitored and controlled may be measured from the shape, amplitude and the variation differing from the normal rhythm (arrhythmia)
So-called pulse monitors, which are in use today, are based on recognizing heartbeats by means of a separate sensor placed on the chest, as the strongest EKG signal may be detected on the chest. Typically, a sensor is a solid, elastic band by shape, the tightness of which is regulated with an elastic ribbon. Electrodes in the band are generally made of electro-conducting plastic. Especially during long-term performances, and while sweating a lot, the band slips away from its place or it may feel uncomfortable or cause abrasions. The measuring of pulse is generally based on recognizing the QRS peak being a part of the EKG signal. In a pulse band the measuring is carried out between two electrodes (the unipolar measuring), which is not an absolutely reliable method for recognizing heartbeats, while various movement disturbances may cause to the signal almost identical pulses compared to a heartbeat or parts of it. Bipolar measuring is used in clinical EKG measuring, that is measuring is done with three electrodes, in which case both positive and negative components are included in the signal. Therefore, in the EKG signal, in addition to the QRS peak, also other essential shapes of the heartbeat are visible, such as the so-called P-wave and the ST-segment. While using three electrodes, the EKG signal may be measured by means of various, so-called Beethoven connections, either separately or simultaneously. In various connections different characteristics of the heartbeat are emphasized, what makes it easier to examine the function of the heart including the recognition of individual heartbeats.
Measuring pulse during sports in water, such as swimming, is especially inconvenient by means of a pulse band. While moving in water, water has access between the skin and the pulse band, and the impurities in water (salt, chlorine and etc., among others) cause a short circuit between the electrodes of the pulse band, in which case the measuring signal is disturbed. In addition, the resistance of water flow tends to move the pulse band on the chest along the body downwards, due to which the pulse band is inconvenient to use. The measuring of the pulse of swimmers with present methods is carried out by interrupting the swimming at the ends of the pool where the swimmer or an assistant uses a separate hand-held band for measuring. Therefore, the interruption of the performance does not give correct information about the pulse rate of the swimmer and is impractical.
Electrodes used in clinical measurements are attached with adhesive or with a suction cup onto the skin, and the quality of the signal is secured with a special gel or similar improving conductivity. In use outside clinical environment, for example during a physical exercise, these kinds of electrodes have proved to be impractical despite of their reliability.
The object of the invention is to provide a method for recognizing and measuring of heartbeat, in which method disadvantages connected with present methods are eliminated. Especially, the object of the invention is to provide a method in the use of which reliable measuring results may be gathered not only from the chest area but also from elsewhere. Furthermore, the object of the invention is to provide a method, in the use of which the measuring electrodes stay in place and in reliable contact also during a long-term measurement and during various movement disturbances. The object of the invention is also to provide a user with options which are easier to use and more advantageous for measuring the pulse.